1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus and particularly, is preferably applied to a sheet processing apparatus for use in the image forming apparatus such as a copying machine, or a laser beam printer.
2. Description of the Related Art
Conventionally, a book-binding machine which binds sheets discharged from an image forming apparatus such as a copying machine, or a laser beam printer into each sheet bundle and folds the bound sheets into a pamphlet by a folding roller has been provided.
However, when a book binding process is carried out on a sheet bundle comprised of a multiplicity of sheets or sheets having a high rigidity by such sheet processing apparatus, a portion folded by a folding roller sometimes may be swollen thereby the quality dropping as shown in FIG. 16.
Thus, to press the swelling of the folded portion, as shown in FIG. 17, there has been available a method of pressing the folded portion to intensify its folding to reduce the swelling by moving a press roller (pair of press rollers 1201) over the folded portion (see Japanese Patent Application Laid-Open No. 2005-089100). This patent document describes technology for suppressing the swelling of the folded sheet bundle.
However, in recent years, in the image forming apparatus including the sheet processing apparatus, increase of production has been demanded regardless of the sheet size. Further, the sizes of the image forming apparatus and the sheet processing apparatus need to be suppressed to minimum ones.
FIG. 18A shows a state in which a folded sheet bundle S100 long in its width direction is discharged from a pair of discharge rollers 827. The right side of FIG. 18A is the front side of the apparatus and the left side is its rear side. In the conventional press operation, if the standby position of a press unit 1200 exists on the rear side (left side in FIG. 18) of the apparatus, after the sheet bundle S100 advances into the press unit 1200, the press unit 1200 moves to the front side (right side in FIG. 18) while the folded portion of the sheet bundle S100 is pressurized by the pair of the press rollers 1201.
After the press operation is finished, as shown in FIG. 18C, the press unit 1200 is moved to the front position of the apparatus which allows the sheet bundle S100 to be discharged in order to discharge the sheet bundle into a discharge tray. However, this state requires the length in the width direction of the apparatus to be increased by the size L1 of the press unit 1200 thereby enlarging the apparatus.
On the other hand, although a method of returning the press unit 1200 to a position which allows the sheet bundle S100 to be discharged (rear side of the apparatus), this method takes a time for the press unit to return to its original position thereby inducing a drop in productivity.